What is periodic cavitation

Could you specify where exactly cavitation occurs? Does it happen periodically? Cavity cavitation is caused by the rotation of the water flow within the tailwater pipe, which creates a vacuum in the central cavity. The main reason is that the turbine operates under conditions other than those for which it was designed (beyond the 5% output limit of the turbine), which damages its normal outlet and leads to flow separation and vortices. Together with the rotating water flow at the entire turbine outlet, this creates a vortex zone at the turbine outlet and the inlet of the tailpipe, where a large pressure drop occurs. When this pressure drops to the vaporization pressure, cavitation occurs. This vortex band rotates within the tailwater pipe at a certain frequency; the vacuum zone at its center periodically impacts the surrounding areas of the tailwater pipe, causing cavitation damage to the pipe walls. This results in periodic pressure fluctuations that give rise to intense noise, sounds of metal striking against each other, rumbling noises, or thunder-like sounds. In severe cases, discharge and flashing phenomena may occur, and these conditions can lead to severe vibrations in the turbine unit, affecting its stable operation. Cavitation in cavities usually occurs on the inner side of the turbine housing ring and in the upper part of the tailwater pipe.